ON and OFF field potentials in the rat superior colliculus during development

Abstract

The present investigation is aimed at characterizing the development of ON and OFF visually evoked responses in the rat superior colliculus from postnatal day 13 (P13) to postnatal day 25. Depth profiles of field potentials reveal that ON and OFF long latency biphasic field potentials are already present when collicular cells are first responsive to light (P13). There is an inversion in the polarity of these responses as the electrode penetrates the collicular layers, suggesting a synaptic organization similar to the one found in adult animals. At P15, OFF field potentials begin to exhibit oscillatory activity. Local cobalt injections within the superior colliculus abolishes these OFF oscillations, suggesting a postsynaptic origin. Fast Fourier transform (FFT) analysis of the OFF field potentials demonstrates that oscillatory activity increases in frequency during development. This increase is thought to reflect the myelination and stabilization of synaptic connections that occur during this period. To our knowledge, this is the first report of OFF oscillatory responses in the superior colliculus.

Patterns of Synchronization in the Superior Colliculus of Anesthetized Cats

“…Correlated discharges have also been described in saccade-related activity recorded from the monkey SC (Istvan and Munoz, 1997). Finally, an oscillatory modulation of visual responses has been observed in the midbrain of several other species, such as rats (Fortin et al, 1997), mice (Masu et al, 1995), and toads (Schwippert et al, 1996). Taken together with our present results, these data provide evidence that oscillatory patterning and response synchronization are prominent features of visual midbrain activity in many vertebrate species.…”

“…Third, synchronization by a common external source cannot account for the fact that synchronization occurs between superficial and deep collicular layers, because superficial and deep SC receive their input from quite distinct sources (Edwards, 1980;Stein and Meredith, 1991). Complementary evidence for intracollicular synchronizing mechanisms has been provided by Fortin et al (1997), who studied oscillatory field potentials recorded in the SC of rats.…”

Developmental changes in BDNF protein levels in the hamster retina and superior colliculus

“…RGC axon synaptogenesis continues into at least the third postnatal week (Lund and Lund, 1972;Warton and McCart, 1989;Campbell et al, 1984). Neurophysiological recordings in rats show that although the onset of synaptic transmission by retino-SC axons begins at very early stages (Reece and Lim, 1998) synaptic responses mature at least through stages corresponding to the third postnatal week in hamsters (Fortin et al, 1997). Neurotrophins, including BDNF, can modulate synaptic efficacy (Thoenen, 1995;Snider and Lichtman, 1996;Shatz, 1997;Schuman, 1999;Turrigiano, 1999;Poo, 2001).…”

Visual Awareness Due to Neuronal Activities in Subcortical Structures: A Proposal

“…Stimulus-dependent oscillatory activities, mostly in the alpha and beta frequency ranges, but also in the gamma range, have been recorded in the optic tectum (or superior colliculus) of several species, including toads (Schwippert, Beneke, & Ewert, 1996), pigeons (Neuenschwander & Varela, 1993;Neuenschwander, Engel, König, Singer, & Varela, 1996), rats (Fortin, Itaya, Chemtob, & Molotchnikoff, 1997), and cats (Mandl, 1993;Brecht & Engel, 1996;Brecht, Singer, & Engel, 1998. The only studies in which both a qualitative and quantitative assessment of the degree of synchronization between activities at different sites was performed are those of Neuenschwander et al (1996), in the pigeon OT, and Brecht and Engel (1996) and Brecht et al (1998Brecht et al ( , 1999, in the cat SC, and these two studies are discussed here.…”